Air conditioning systems are installed in vehicle cabins for controlling air conditioning in the vehicle cabins to thereby maintain occupant comfort therein.
Each of the air conditioning systems is normally designed to move an air mix damper, in other words, an air mix door, to an appropriate position to adjust the amount of air passing through a heater core to control the temperature of air blown out from the corresponding air conditioning system, thus controlling air conditioning in the vehicle cabin.
For such an air conditioning system, there are needs to provide occupant comfort in the vehicle cabin as soon as possible, and to reduce occupant's operations of the air conditioning system. If air conditioning systems meet these needs, they can enhance their marketability. An example of an air conditioning system aiming to meet these needs is known in Japanese Patent Application Publication No. H08-276718.
The known air conditioning system installed in a vehicle is provided with means for storing therein preset temperatures as cabin temperatures corresponding to running conditions of the vehicle; the running conditions include cabin temperatures, outside temperatures, amounts of solar radiation, and vehicle speeds. Even if a current running condition is changed to another running condition, the storing means permits a driver to run the vehicle under a suitable cabin temperature that meets the changed running condition without occupant's changing operations of the preset temperatures. Specifically, the known air conditioning system is designed to receive a temperature Ts set by a temperature setter, and read out one of the preset temperatures Ts′ stored in the storing means if the temperature Ts matches a predetermined reference temperature. Then, the air conditioning system is designed to control the cabin temperature based on the preset temperature Ts′ read from the storing means. The disclosed design of the known air conditioning system provides occupant comfort without occupant's changing operations of the preset temperatures.
In engine-driven vehicles, air conditioning systems use the residual heat from their engines as the heating energy of air conditioning. Increasing engine efficiency of the engine-driven vehicles reduces the residual heat from their engines. Thus, an increase in fuel consumption is required to increase the heating energy of air conditioning, resulting in reduction of gas mileage.
In electric vehicles, such as electric-powered vehicles and hybrid vehicles, air conditioning systems usually use electric heaters, such as PTC (Positive Temperature Coefficient) heaters, heat pumps with electric compressors, and the like as a heating source. Thus, an increase in power consumption by the electric heaters is required to increase the heating energy of air conditioning, resulting in reduction of electric mileage.
Then, in order to improve gas mileage or electric mileage, one type of air conditioning systems is designed to calculate an amount of heat currently needed, and operate a heating source by a minimum amount of power, i.e. a minimum amount of fuel or a minimum amount of electric power, required to generate the amount of heat currently needed without operating its heating source by a large amount of power required to generate a sufficient amount of heat.